The present invention relates generally to medical devices for detecting cardiac disease. More particularly, the present invention relates to medical devices for detecting vulnerable plaque within a blood vessel.
Therapy modalities for heart disease have traditionally focused on treating blood vessels which have become occluded (blocked) or stenotic (narrowed) by calcified plaque deposits. Blood vessels which have become occluded or stenotic in this manner may interrupt the flow of blood which supplies oxygen to the heart muscle. Occluded or stenotic blood vessels may be treated with a number of medical procedures including angioplasty and atherectomy. Angioplasty techniques such as percutaneous transluminal angioplasty (PTA) and percutaneous transluminal coronary angioplasty (PTCA) are relatively non-invasive methods of treating restrictions in blood vessels. In these procedures, a balloon catheter is advanced over a guidewire until the balloon is positioned proximate a restriction in a diseased vessel. The balloon is then inflated and the restriction in the vessel is opened. During an atherectomy procedure, the stenotic lesion is mechanically cut or abraded away from the blood vessel wall using an atherectomy catheter.
Calcified plaque deposit typically comprise hard materials. Plaque may also comprise soft materials or combinations of soft and hard materials. Soft plaque typically comprises deposits of cholesterol and other fats which build up within the blood vessels as a patient ages. The build up of plaque in the blood vessels is sometimes referred to as atherosclerosis, or hardening of the arteries.
Atherosclerosis often begins as a small injury to an artery wall. This injury triggers a cyclic cascade of injury and response, inflammation, and healing, which may ultimately lead to the narrowing of the artery. As the atherosclerotic plaque worsens, inflammatory cells, especially macrophages, collect at the site to isolate the debris of the damaged tissue. The result is a core of lipid, macrophages or foam cells and nectrotic tissue, covered by a fibrous cap of scar tissue. If the fibrous cap becomes weakened or is subjected to excessive stress, it may rupture, exposing the trombogenic contents of the core to the blood stream. If the resulting blood clot is severe enough, it may occlude the artery. If this obstruction persists in a coronary artery, a myocardial infarction may result.
Plaque deposits which are at risk of rupturing are sometimes referred to as vulnerable plaque. Vulnerable plaque typically comprises a core of soft materials covered with a fibrous cap. Many vulnerable plaque deposits do not limit the flow of blood through the blood vessels. It has recently been appreciated that vulnerable plaques which do not limit flow may be particularly dangerous because they produce no warning symptoms, but can rupture suddenly causing heart attack and death. This may occur, for example, when the vulnerable plaque ruptures, a blood clot may be formed inside the blood vessel lumen causing a blockage.
Recently, the pivotal role of inflammation in the progression of atherosclerosis has been recognized. A systemic increase in temperature is often associated with infection (e.g., a fever). Likewise, a local infection or localized damage to tissue may result in a localized increase in temperature. An increase in temperature is thought to be caused by the response of the immune system to infection, known as inflammation. It has been observed that the inflamed necrotic core of a vulnerable plaque maintains itself at a temperature which may be one or more degrees Celsius higher than that of the surrounding tissue. For example, an inflamed plaque in a human heart, where the normal temperature is about 37xc2x0 C. may be at a temperature as high as 40xc2x0 C.
The present invention relates generally to medical devices for detecting cardiac disease. More particularly, the present invention relates to medical devices for detecting vulnerable plaque within a blood vessel. A system in accordance with the present invention includes a first wire having a distal end coupled to a voltage source and a proximal end coupled to an instrument capable of measuring voltage. A distal end of a second wire is also coupled to the voltage source and a proximal end of the second wire is coupled to the instrument. The amplitude of the electromotive force produced by the voltage source preferably varies with the temperature of a tissue proximate the voltage source.
One embodiment of system in accordance with the present invention includes a guidewire including the first wire and the second wire. In this embodiment, a distal end of the first wire and a distal end of the second wire are coupled to form a junction. In a preferred embodiment, the first wire comprises a first material and the second wire comprises a second material which is different than the first material. Also in a preferred embodiment, the first material and the second material are selected so that an electromotive force is produced across the junction therebetween. In a particularly preferred embodiment, the first material and the second material are selected so that the amplitude of the electromotive force across the junction varies with changes in the temperature of the junction. Also in a particularly preferred embodiment the amplitude of the electromotive force produced by the junction varies with the temperature of a tissue proximate the voltage source (i.e., the temperature of the junction is effected by the temperature of tissue proximate the junction).
An additional embodiment of system in accordance with the present invention includes a catheter including a first wire having a distal end coupled to a detector and a proximal end coupled to an instrument. The catheter also includes a second wire having a distal end coupled to the detector and a proximal end coupled to the instrument. In a preferred embodiment, the detector produces a voltage which varies with the temperature of tissue located proximate a balloon of the catheter. The detector may comprise, for example, a photodiode. In this embodiment, the catheter also includes an optical fiber having a proximal end that is coupled to a light source. Light from the light source passes through optical fiber, and is collimated by a lens. This light is partially reflected by a partially reflecting surface of a reflector so that it illuminates a portion of a layer of the balloon. The layer of the balloon preferably has temperature dependent optical properties which may effect, for example, the wavelength and/or intensity of the light which is reflected by layer. The portion of the light which is reflected by this layer forms a light signal. At least a portion of this light signal passes through the partially reflecting surface of the reflector and illuminates the detector.